3D-Printed Implant Heals Severed Spinal Cord

Researchers at the University of California, San Diego, created a 3D-printed spinal cord implant that help heal spinal injuries and markedly restores neural functioning. The implant shields neural progenitor cells while also directing orderly growth of axons.

by Lina Zeldovich

February 11, 2019

A team of researchers at the University of California, San Diego, has created a 3D-printed spinal cord implant that helps heal traumatic spinal injuries and markedly restores neural functioning. Loaded with neural progenitor cells, the implants achieved significant recoveries in injured rats.

More than 500,000 people in the U.S. suffer from various spinal cord injuries. Most of these injuries originate from car accidents; falls from ladders, stairs and other heights; and knife wounds. Besides the significant psychological and economic cost, these injuries rob patients of their mobility, affect their fine motor skills, cause pain and suffering, and degrade their overall quality of life.

When trauma impacts or crushes a spinal vertebra, the spinal cord compresses. This damages or destroys the axons, the threadlike parts of nerve cells that communicate and propagate impulses to other cells. In a healthy human body, the axons grow in a very specific, orderly, linear pattern from rostral to caudal, or, in lay terms, downward “from head to tail.”

This orderly orientation is crucial to central nervous system function, said Jacob Koffler, assistant project scientist at the Neural Tissue Engineering Lab of the UCSD’s Medical School and the study’s author.

When the body tries to regrow the axons at the site of the injury, the new axons lack the proper organization, so the normal nervous system functioning does not get restored. In recent past, researchers have tried using stem cells to repair spinal cord damage, but they didn't survive in the toxic, inflammatory environment of a spinal cord injury, Koffler said.

To solve this problem, the team created a specialized implant that could shield the neural progenitor cells while also directing the axons’ orderly growth.

UCSD’s scientists built the implant using a special 3D printer called a microscale continuous projection printing method (μCPP). Most 3D printers use extruders or nozzles to deposit materials one layer at a time. The μCPP relies on light to create solid blocks of structures in one iteration rather than layering them up. By using a MEM chip containing 2 million micromirrors the printer reflects light into a solution to polymerize a hydrogel scaffold.

“That allows us to print in blocks because we move the focal plane of the light,” said Shaochen Chen, professor at the Nanoengineering Department at UCSD, and the study’s co-author.

The team printed the implantable scaffold to contain dozens of linear micro channels that would direct the axons to naturally align in rostral-to-caudal fashion. The channels, which were twice the width of a human hair, were then loaded with neural progenitor cells.

The researchers then implanted the scaffolds into rats that had a piece of their spinal cord removed, creating a gap in the spinal column. This rendered them immobile.

When researchers implanted the micro-channel scaffolds, the animals exhibited a remarkable recovery. Within five months, they were able to move three joints—ankle, knee and hip. The next step would be to achieve enough regeneration to enable the animals to bear weight and stand on their legs, Koffler said.

This recovery was possible for two reasons. One is because the new axons aligned in the proper direction, guided by the scaffold’s channels. The second is because the neural progenitor cells were shielded from the inflammatory environment of the injury. Within a month of the operation, neural progenitor cells had survived in every grafted animal and completely filled the scaffold channels.

Koffler and Chen noted that choosing the right material to build the scaffolding was important. Some materials did not hold up long enough and deteriorated within four weeks. The team settled on the type of hydrogel called polyethylene glycol–gelatin methacrylate.

Another advantage of this μCPP technology is printing scaffolds very quickly and tailoring them to patient-specific anatomy, reconstructed from X-Rays and MRIs. The technology may be ready for clinical trials relatively soon.

“First we need to go though the large animal models, which is what we are working on starting now,” Koffler said. “It’s probably at least five years before we can apply for clinical trials.”